This invention relates to an automatic gate opening apparatus which has provision for shut off when an object such as a person or a vehicle blocks the movement of the gate. The invention also incorporates means for authorized persons to manually open or close the gate in the event of a power failure.
Many power operated gate mechanisms have been developed; these have generally made use of a motor operated linkage which attaches to the gate and extends outwardly to move the gate on its hinges. The gate may be of the horizontally-opening, vertically withdrawn type or it may involve a turnstile or a horizontally sliding barrier. The automatic extension of a link arm in the prior art constitutes a hazard to an unwary person standing out of the way of the gate but still within contact range of the link arm. The gate itself presents a similar safety problem should it come in contact with a person standing in its path. In addition to doing bodily harm, the gate mechanism may itself be damaged when its motor is stalled to the point of overheating or its gears stripped if the drive mechanism develops excessive torque.
A further problem in the prior art is the complexity and expense of the gate opening apparatus. In efforts to provide sufficient power and safety, previous designs use relatively intricate mechanisms which are costly, complex to install and hard to repair in case of breakdown. The gate actuators of Richmond (U.S. Pat. No. 4,403,449), Duncan (U.S. Pat. No. 4,735,018) and Fior (French 2,481,351) utilize external extension arms for which additional actuating space outside of the roadway is required. The fact that these gate operators are most conveniently driven by a rotary power source such as an electric motor requires relatively elaborate linkages to convert the initial rotation to gate-activating motion. This can also be seen in the operators of Reid (U.S. Pat. No. 4,503,723), Gute (U.S. Pat. No. 3,284,950) and Weiss (U.S. Pat. No. 4,848,175). The manufacture, installation and maintenance of these operators are costly and normally confined to expensive fences and walls.